The role of diversity for collective bacterial migration through diverse environments

Chemotactic bacteria form expanding wave fronts that allow populations to achieve directed expansion towards new territory (Adler J. Science 1966), which can enhance total population growth. But even isogenic populations exhibit phenotypic heterogeneity in their chemotactic properties, and it has been unclear how this affects their directed expansion with growth. We recently showed that diverse cells can travel together in the expanding front by sorting themselves by chemotactic ability, which compensates for their differences by matching ability to the local chemotactic signal (Fu, Kato et al. Nature Communications 2018). However, this places the lowest-performing cells at the back of the wave and at highest risk of falling behind. Here, through a combination of simulations and theory, we demonstrate the conditions in which diversity is valuable (or not) for collectively-migrating populations that grow and encounter varying environments during travel.